blown head gasket
 

Today while running at 65mph turning 4800 rpm I had a sudden rpm loss of about 700 rpm then suddenly a valve tapping noise, got home pulled the port side valve cover everything looked ok, pulled the plugs all looked ok except 5 looked a little darker, checked compression and found no compression on 5 and 7 . screwed a plug in 7 and got a little compression on 5 and vice a versa, i feel pretty confident that i have a blown head gasket , but my question is why / this is a fresh motor that i finished in november and just turned 30hours,,, any ideas/

Re: blown head gasket
 

What head gasket did you use?

Re: blown head gasket
 

When you rebuilt it 30 hours ago, did you deck the block and heads or at least confirm that both surfaces were flat? Did it ever overheat real bad since you rebuilt it? May well be a blown head gasket. That usually doesn't make a sound like a valve ticking, but it's a boat! S**t happens!

Re: blown head gasket
 

I did deck the heads and block, and no the engine has not over heated, the way i determined that the ticking was a valve was. when i was checking the running at home i brought the motor up to 2500 rpm and started pulling plug wires to find what was firing or not.When i pull 5 the ticking sound stops and it the sounds like its comming from 7 though,when i pull 7 off no change. the motor was put together with stock cam lifters and valve springs. i was thinking while i have to pull it down anyway, Anybody have any sugestions on cams and lifters

Re: blown head gasket
 

Use Cometic head gaskets when you put it back together and torque the heads carefully. As for a cam recomendation, we would need a lot more input, which motor, specs, heads, efi? carburated?.

Ray @ Raylar

Re: blown head gasket
 

It's hard to diagnose your ticking sound long distance but it could be a leaking exhaust manifold. someone just went through this on oso a few months ago where the ticking noise went away when he pulled a particular spark plug. Problem was a leaking exhaust manifold gasket. i was involved in that thread. If curious you could search my posts for the particulars. Just trying to help.

Re: blown head gasket
 

What I meant to say above was when a particular spark plug WIRE was pulled. I know you know what I meant. I shouldn't have been trying to do three things at once!